Defrost control for refrigeration systems



Feb. 27, 1951 c. A. SMITH 2,543,133

DEFROST CONTROL FOR REFRIGERATION SYSTEMS Filed April 6, 1950 5 Sheets-Sheet l Feb. 27, 1951 c. A. SMITH DEFROST CONTROL FOR REFRIGERATION SYSTEMS Filed April 6, 1950 I 5 SheetsSheet 2 BWMK,

Feb. 27, 1951 c. A. SMITH 2,543,133

DEF'ROST CONTROL FOR, REFRIGERATION SYSTEMS Filed April 6, 1950 5 Sheets-Sheet 3 67 #5 I! k I. Z5

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Feb. 27, 1951 c. SMITH 2,543,133

DEF'ROST CONTROL FOR REFRIGERATION SYSTEMS Filed April 6, 1950 s Sheets-Sheet 4 Feb. 27, 1951 c. A. SMITH DEFROST CONTROL FOR REFRIGERATION SYSTEMS 5 Sheets-Sheet 5 Filed April 6, 1950 mm W W5 H /H 0 m 9,

r a a 37M 3 79 Mp1 MU. 4 a 6 w w W. 8 6 j H30 g M w u 7 W w 4 a m 9 0 a m o m 0 W 4 7 H a. I 2 MW Patented Feb. 27, 1951 DEFROST CONTROL FOR REFRIGERATION SYSTEMS Carl A. Smith, Ferguson, Mo., assignor to Missouri Automatic Control Corporation, St. Louis, Mo a corporation of Missouri Application April 6, 1950, Serial No. 154,230

This invention relates generally to control devices for refrigeration systems which employ a compressor for compressing a gaseous refrigerant, a condenser for cooling and liquefying the refrigerant and an evaporator coil wherein the refrigerant vaporizes and expands to cool the coil and the surrounding area to be refrigerated and is thereafter periodically returned to the compressor to again be compressed. It more particularly concerns an automatic defrost control device adapted to be used in a system as above for periodically interrupting operation of the compressor for an interval suflicient to permit the temperature of the evaporator coil to rise to a point wherein any frost accumulations thereon will be melted and in which this interval is terminated in response to a predetermined increase in the refrigerant pressure in the return conduit from the evaporator to the compressor.

The normal operation of the compressor in such systems is usually intermittent and is ordinarily controlled by a normal operation control device which may be responsive to either the temperature of the space to be refrigerated, the temperature of the evaporator coil or the pressure of the refrigerant in the return line to control operation of the compressor so as to maintain a preselected temperature of the refrigerated space. The automatic defrost control device in the present invention is arranged to override such normal operation control devices and to interrupt compressor operation at preselected intervals for a period sufllcient to insure defrosting of the evaporator and is responsive to restore control of the compressor to the normal control device only at a pressure which is substantially higher than the high pressure or corresponding high temperature to which the normal control device responds to start operation of the compressor.

It is an object of the present invention to provide a generally new and improved fully automatic defrost control device of the above character which is capable of initiating defrost periods at preselected intervals and is operative to terminate the defrost periods in response to a predetermined fiuid pressure.

A further object is to provide an automatically operated, heavy duty, double break switching device having a snap action in both directions suitable for the control of a refrigeration compressor circuit in which the switch is caused to be actuated to a circuit breaking position at a preselected time by a chronometric device and in which the switch is subsequently caused to 7 Claims. (Cl. 181-1) be actuated to a circuit closing position in response to a predetermined increase in the pressure of the refrigerant in the return line between the evaporator and the compressor.

A further object is the provision of a refrigeration defrost control having switch structure which is normally biased in one operative position by resilient means and in which the energy of a low torque synchronous timing motor is accumulated over a period of time to be released ata predetermined time to oppose said resilient means and cause actuation of the switch to an opposite position with a snap action and wherein said resilient means is restrained by latch means and is subsequently released in response to a predetermined fluid pressure to cause the switch structure to be again operated to the first position with a snap action by the resilient means.

Further objects and advantages will become apparent upon reading the following description and accompanying drawings.

In the drawings:

Fig. 1 is a diagrammatical illustration of a refrigeration system in which is incorporated a defrost control device constructed in accordance with the present invention;

Fig. 2 is a front elevation of the defrost control device shown in Fig. 1;

Fig. 3 is a side elevation of the defrost control device shown in Fig. 1;

Fig. 4 is an enlarged left side elevation of the control shown in Fig. 2 with its casing shown in cross section;

Fig. 5 is a right side elevation of the control shown in Fig. 2 with its casing removed;

Fig. 6 is an elevation of the control shown in Fig. 2 with its casing removed;

Fig. '7 is a top view of the control shown in Fig. 2 with its casing removed;

Fig. 8 is a rear elevation of the control shown in Fig. 2 also with its casing removed;

Figs. 9 to 12 inclusive are different operative views of the switch actuating mechanism and are taken generally on line 9-9 of Fig. 4;

Fig. 13 is a slightly enlarged sectional view showing the main shaft and cam arrangement and is taken on line Iii-l 3 of Fig. 6;

Fig. 14 is a perspective view of the pressure actuated trip lever;

Fig. 15 is a perspective view of the cam actuated trip lever;

Fig. 16 is a perspective view of the switch actuating lever; and

Fig. 17 is a perspective view of the spring loading lever.

The refrigeration system diagrammatically illustrated in Fig. 1 includes as primary elements a compressor l0. an electric compressor driving motor II, a condenser l2, a receiver lland an evaporator coil ll. The output side of the compressor I is connected to one end of the condenser by conduit i and the other endof the condenser is connected to one end of the receiver II. The other end of the receiver is connected to the evaporator coil H by a conduit |5. Interposed in the conduit I5 is a conventional thermostatically controlled expansion valve |1 having a temperature sensitive bulb l5 located so as to be sensitive to the temperature of the evaporator ll. The lower end of the evaporator coil is connected to the intake of the compressor by a conduit I5. I

The electric driving motor H is provided with an energizing circuit comprising the leads 20 and 2| which are connected to a suitable source of electrical power. Interposed in the leads 25 and 2| is a'conventional normal operation control device generally indicated at 22 which functions to control the normal operation of the compressor in accordance with cooling requirements and may be a pressure actuated switch as shown in the illustration which is responsive to the pressure of the refrigerant in the return line l9 between the evaporator and the compressor. The control 22 is also indicated as being a double break switching device in which both sides of the circult are broken.

Also interposed in the compressor motor circult and in series with the normal control device 22 is a defrost control device generally indicated at 23 which is constructed in accordance with the present invention. A manually operated master switch is also provided for control of the compressor motor circuit and is indicated at 24. The defrost control device 23 includes a frame comprising a rear panel member 25 and a front panel member 25 which are spaced and securely connected at several points as by spacers 21 and screws 2111. At their lower right hand corners the panel members 25 and 25 have integral portions 28 and 29 formed horizontally at right angles therewith and have attached thereto as by screws 35 the flange of a cup element 3|. Mounted on the upper right hand corner and on the front side of rear panel 25 in Fig. 6 is an electrically operated synchronous timer motor' generally indicated at 32. The motor has 8. casing 33 provided with perforated ears 34 through which pass screws 35 for attachment of the motor to the rear panel member 25. The timer motor may be of conventional commercial type which includes speed reduction gearing contained within the casing 33 and has a power take off shaft 35 projecting rearwardly through the rear gear 35. Between the pinion gear 31 and the spur gear 39 is an intermediate gear 40 mounted for rotation on a shaft 4| which is supported in the rear panel 25. The gears 31, 39 and are in mesh as indicated in Fig. 8 and the shaft 38 is thereby driven by the synchronous motor 32. The intermediate gear serves to further reduce the speed of the shaft as is apparent. The shaft 35 also extends forwardly of the front panel 25 and has rigidly attached to its end as by a set screw 42, a knurled hub member 53. Rigidly attached to the inner end of the hub member 43 as by riveting at 44 is a disc like dial 55 having the periphery on its front side divided into 2-4 equal divisions representing hours. Surrounding the shaft 25 and extending between the hub member 43 and the rear panel 25 is an inner sleeve member 45 which carries rigidly attached to its rearward end as by riveting a first trip cam 41. Surrounding the inner sleeve 45 is an outer sleeve 46 which carries rigidly attached thereto at its rearward end a second trip cam 45. Also carried on sleeve 45 and rigidly attached thereto by means of a set screw 55 passing through its integral hub is a double lobed loading cam 5|.

At their forward ends the sleeve members 45 and I carry hub members 52 and 53 respectively rigidly attached thereto as by set screws 52 and 55. The hub members 52 and 53 have rigidly attached thereto as by riveting a pair of adjusting arms 55 and 51 respectively. The outer ends of the adjusting arms are formed over as at 55 and 55 and receive the periphery of the dial 45. There are screws 55 and 5| which pass through these U-formed end portions of the adjustin arms whereby they may be clamped tightly in an adjusted position on the periphery of the dial. The inner and outer sleeves carrying the cams 41 and 49 are therefore driven by the shaft 35 through the dial disc and the adjusting arms. The ends of the adjusting arms which overlay the periphery of the dial are pointed so as to facilitate accurate indexing with lndicia on the dial face. The adjusting arm 55 carries at its inner end a stop pin 52 which is engaged by a projection 63 at the inner end of adjustable arm 51 and which limits the relative rotation of the two adjusting arms. By the arrangement described it will be seen that the second tripping cam 45 and the spring loading cam 5| are fixed with relation to each other and that the first tripping cam 41 which is attached to the inner sleeve 45 may be rotated relative to the second tripping cam 49 and the spring loading cam 5| by rotating the adjusting arm 55. The sprin loading cam 5| is provided with two lobes 5|a and 5| b for a purpose to b explained hereinafter.

Mounted on the upper left hand corner and on the front side of rear panel 25 are two pairs of switch blades 54 and 64a and 65 and 55a which carry contacts 54b and 660 and 55b and 55c respectively. The switch blades are carried on an angle bracket 65 and are assembled, together with suitable spacing insulators on screws 51 by which they are attached to the bracket 55. Provision for adjustably positioning the bracket 55 on the panel is made by providing a slot 55 in the rear panel 25 through which passes a screw 59 and is threadedly engaged in the bracket 56 at one end thereof and a screw 10 passing through a clearance hole in the rear panel and threadedly engaging the bracket at its other end. The resilient switch blades are formed so that the contacts which they carry are normally held open.

Pivotally mounted between the front and rear panels on a pivot 1| which is supported in the panels is a generally L-shaped switch actuating arm 12 which carries at its upper end rigidly attached thereto an abutment element 13 of dielectric material which is adapted to engage the lower switch blades 54a and 55a and to move them upward and to close the contacts as the switch actuating arm 12 is rotated clockwise about its pivot II. Pivoted adjacent the lower end of arm I2 on a pivot I4 which is supported in the front and rear panel members. is a horizontal cam actuated trip arm I5 having a laterally extending platform portion I5 which under certain conditions is abutted at its edge by the lower end of the switch operating arm I2 whereby the arm I2 is restrained from counterclockwise rotation. The

cam actuated trip arm I5 is normally urged in a clockwise direction about its pivot I4 by a spring 11. Arranged generally parallel with the long vertical leg of the switch actuating lever I2 and pivoted at its upper end on a pivot I8 is a spring loading arm I9. The lower free end of the arm I9 lies adjacent the double lobed cam H and as the cam is rotated counterclockwise the arm 19 is rotated counterclockwise about its pivot I8. The arm 19 is provided with a lateral portion 80 which is engaged by the lobes of cam H. The lateral portion 80 of arm I9 has a cut out portion 80a for a purpose to be described later.

The spring loading arm 19 has pivotally attached thereto on a pivot 8|, a pin 82 which extends horizontally through an aperture in the switch actuating lever I2 and has a nut 83 on its outer threaded end. The pin 82 is provided with a collar or flange 84 at its inner end and a coil spring 85 is provided which surrounds the pin- 82 and bears against the collar 84 at one end and the switch actuating lever I2 at its other. A spring 85 attached at one end to the arm I2 and at its other end to an anchor pin 81 mounted in the panel members, urges the arm I2 in a clockwise switch closing direction. The spring 85 is,

however, considerably stronger than the spring 86 and is capable of readily overcoming it. The pressure actuated trip arm I5 carries at its outer end a roller 88 adapted to be engaged by the lobes of cams 41 and 49 which as these cams are rotated counterclockwise cause the trip arm I5 to be rotated counterclockwise, thereby causing the lower end of arm I2 to become disengaged from the horizontal portion I8 of the trip arm.

Mounted in the cup element 3 I see Fig. 10, is a colla'psible bellows 09 having its upper end firmly attached and sealed to the inner wall of the cup element 8| at 90 and having its lower end movable. The lower end of the cup element 8| is provided with a suitable fitting 9| for the purpose of attaching a conduit 92, see Fig. 1, by which the cup element is connected with the return line from the evaporator coil to the compressor at 93. There is an adjustable bellows stop screw 95 threadedly engaged in the fitting 9I for limiting the downward travel of the lower free end of the bellows. The stop screw 95 has a sinall longitudinal passage 96 therethrough and a connecting,

cross passage 95a therethrough tQ provide communication to the interior of the cup element.

Resting on the inner side of the lower free end of the bellows and extending upwardly therefrom is an actuating pin 91. The pin 91 is guided in a bushing 98 carried by a horizontal plate 99. The plate 99 is clamped between the flange of the cup element and the lower horizontally formed portions 28 and 29 of the rear and front panel members. Mounted above the bellows 89 on a pivot I00 is a horizontally arranged pressure actuated trip lever IOI. The upper end of actuating pin 91 engages the under side of lever IOI immediately to the right of its pivot I00 and causes its counterclockwise rotation when a predetermined pressure increase is communicated to the lower part of cup element 3| causing the bellows 89 to be contracted and the actuating pin 91 to be moved upward. At its right end the pressure actuated trip arm IOI is engaged on its upper side by an adjustable pressure opposing spring I02. Tension of spring I02 is made adjustable by the provision of an internally threaded sleeve I09 bearing against the upper end of the spring and by an engaging threaded adjusting screw I04 which is rotatably mounted in a bracket I05 attached to the rear panel 25 as by screws I06. The left hand end of pressure actuated trip lever IOI is forked as at l0la and receives the stem of a vertically acting latchmember I01. Latch member I01 is guided vertically as by slots I08 in the latch which receive horizontal guide pins I09 supported in a bracket H0. The latch I0! is normally urged upward bya spring III which bears against a flange II2 on the stem thereof. The upper end of latch I0I is adapted to engage the lower free end of the spring loading arm I9,

as indicated. The upper end of the latch member N1 is beveled as at II3 so that as the arm I9 is rotated counterclockwise by the cam 5| it may depress the latch and be permitted to move into a latched position.

There is a rectangular cut out in the left hand side of rear panel 25 in which is mounted as by rivets 4, a terminal panel II5 of dielectric material, see Figs. 6 and 8. Mounted in panel H5 are terminal posts H8 to which external main leads 20 and 2I are connected on the front side of the panel and to which internal wiring leads 20a, 20b and 2Ia, 2Ib are connected on the rear side. The internal leads 20a, 2012, H11 and 2Ib are connected at their other ends to the switch blades 64, 84a, and 65a respectively. A parallel circuit for continuous energization of the synchronous timer motor 32 is provided by the internal leads 20c and 2Ic which connect the motor across the main leads 20 and 2| as shown in Fig. 8. There is also a resistor ll8a interposed in the lead 200 which may be provided to drop the voltage so as to accommodate commercially available synchronous motors.

The defrost control device 23 is provided with a rectangular open front casing I I1 having a back and four sides and a front cover member II8 the casing as by riveting, see Fig. 4. It is also attached to the lower side of the casing as by screws I23 and feet I24 which are formed as part of the plate member 99, see Figs. 10 to 12. The cover member II8 has a round window I25, see Fig. 4, concentric with the dial 45 which is provided with a' transparent plastic disc I28 attached to the cover as by rivets I2I. The plastic disc has a central aperture through which projects the knurled hub member 43. There is also provided a fixed index pointer I28 which is attached to the front panel member 28 as by a rivet I29 and which has a pointed end which under lies the transparent window.

In operation cated by the arrows.

7 the timer motor to the shaft 38 may be varied to suit requirements, in the present arrangement the gear reduction is such that the shaft 38 makes one revolution in 24 hours.

Referring to Fig. 9 in the drawings; in this operative view the defrost control is. inoperative to aifect the compressor motor circuit and operation of the compressor is therefore under control of the normal control device 22. The switch contacts Bib-84c and Bib-45c being closed by reason of the return spring .8. The spring loading arm I8 is resting on a low point of the cam Ii thus permitting the spring It to rotate the switch actuating lever I2 clockwise to close the switch contacts. The pressure actuated trip arm is shown rotated, due to pressure acting through the pin 8i,'to a position in which the latch illl is moved downward out of engagement with the spring loading arm I8, and the cam actuated trip lever 15 is in its normal horizontal position with its follower roller 88 riding the lower parts of cams 41 and 4a. In this position the lower end of switch actuating arm 12 will, of course, engage the horizontal portion 16 of the cam actuating trip lever 15.

In Fig. 10, the rotation of shaft 38 has progressed to a point wherein lobe Bio of the cam Ii has moved the spring loading lever 19 counterclockwise to a point wherein the latch member ifll is now engaging its lower end and wherein the relatively strong spring 85 is compressed. Also in this position the pressure actuated trip lever III has been rotated to its normal horizontal position by the spring I82 which is permitted as a consequence of a decrease in pressure in the lower part of cup element 3| acting on the bellows 88. In this position the relatively strong spring 85 is now stressed to a point where it is capable of rotating the switch operating arm I! counterclockwise in opposition to the spring 86 which will result in opening of the contacts.

In Fig. 11, the rotation of shaft 88 has progressed to a point wherein the high point of the lobe iia of cam 5i has cleared the edge of the cut out portion 80a of the lateral portion 8| of the spring loading arm 19 and the trip cam 48 has progressed to a point wherein its lobe is starting to engage the roller 88 of the cam actuated trip arm I5. Other elements of the mechanism remain in the same position as indicated .in Fig. 10.

In Fig. 12, the rotation of shaft 38 has progreased to a point wherein the lobe of tripping cam 49 has rotated the cam actuated trip arm I! counterclockwise moving its horizontal portion I8 out of engagement with the lower end of the switch actuating arm 12 thus permitting the rapid counterclockwise rotation of arm-I2 under the urging of the relatively strong spring 85. When this occurs the dielectric contacting member 13 attached to the upper end of the switch operating arm 12 leaves the lower switch arms a and 85a permitting the switch contacts to part rapidly due to the inherent resiliency of the lower switch blades. The spring loading arm 18, however, is retained in its latch position by the latch ii". In this position the compressor motor energizing circuit is broken and the defrost period is initiated.

During the interval which follows, the pressure in the return line from the evaporator to the compressor, which is communicated to the lower part of cup element 8i, will gradually build up due to inoperation of the compressor and when it reaches a predetermined high point, the opposing spring I02 will be overcome and the pressure actuated trip lever iiii will be rotated counterclockwise about its pivot I00 thereby forcing the latch I01 downward out of engagement with the lower end of the spring loading arm 18. When this occurs the spring 86 is permitted to again return the switch actuating arm rapidly in a clockwise direction causing the switch contacts to be again closed with a snap action and the elements of the mechanism to return to the positions as shown in Fig. 9. The defrost period is thus terminated and control of the compressor operation is returned to the usual normal control device.

The pressure at which the pressure actuated cam iiii trips the latch ill may be varied by varying the tension of the opposing spring I02. This is accomplished by rotating the spring adjusting screw ill. By the provision of the two lobes Ila and Bib on the spring loading cam ii and the provision of the two tripping cams II and is, two defrost periods may be caused to occur at unequal intervals in one revolution of the 24 hour dial. Also by the described arrangement in which the tripcam I1 is angularly ad- Justable with relation to the trip cam 48, the intervals. at which the defrost periods are initiated may be varied.

The foregoing description and accompanying drawings are intended to be illustrative and not limiting the scope of the invention being set forth in the appended claims.

I claim:

1. In a device of the kind described, a control member, a movable actuating member operatively associated with said control member, a first spring for urging said actuating member in one direction, a first releasable latch means operative to restrain movement of said lever in an opposite direction once it has been moved to a predetermined position by said first spring, a cam follower. a second stronger spring operatively connected at one end to said cam follower and at its other end to said actuating member, a first cam for moving said cam follower in a direction to stress said second spring in opposition to said first spring, and for moving it to a position wherein said second spring is stressed a predetermined amount, a second releasable latch means for holding said cam follower in said position once it has been moved to said position, a second cam for releasing said first latch means, means for driving said cams at a predetermined rate of speed, said cams being arranged to act in the order recited, whereby said second spring is first stressed between said cam follower and said actuating member by said first cam and thereafter, said first latch means is released by said second cam permitting said stressed second spring to move said actuating member oppositely against said first spring, and pressure responsive means for releasing said second latch means, thereby to permit the return of said cam follower and' said actuating member by the action of said first spring.

2. In a device of the kind described, a control member, a pivoted lever operatively associated with said control member, a first spring for urging said lever in one direction, a cam follower adjacent said lever, a second stronger spring operatively connected at one end to said cam follower and at its other end to said lever and being capable when stressed of overcoming said first spring, a first releasable latch means operative to restrain movement of said lever in an opposite direction once it has been moved to a predetermined position by said first spring, a first cam for moving said cam follower in a direction to stress said second spring in opposition to said first spring and for moving it to a position in which said second spring is stressed a predetermined amount when said latch means is effective to restrain the opposite movement of said lever, a second releasable latch mean operative to restrain said cam follower against its return from said position once it has been moved to said position, a second cam for releasing said first latch means, a shaft for said cams, means for driving said shaft at a predetermined rate of speed, said cams being mounted for rotation with said shaft and being arranged to act in the order recited when'said shaft is rotated by said driving means, whereby said second spring is first stressed between said cam follower and said lever by said first cam and whereby thereafter, said first latch means is released by said second cam thereby permitting said stressed second spring to move said lever in an opposite direction against said first spring, and a pressure responsive actuator responsive to a predetermined pressure to release said second latch means, thereby to permit the return of said cam follower and said lever by the action of said first spring.

3. In a device of the kind described, a control member, a movable actuating member operatively associated with said control member, a first spring for urging said actuating member in one direction, a first releasable latch means operative to restrain movement of said actuating member in an opposite direction once it has been moved to a predetermined position by said first spring, a cam following member, a second stronger spring operatively connected at one end to said cam follower and at its other end to said actuating member, a first cam for moving said cam follower in a direction to stress said second spring in opposition to said first spring, and for moving it to a position wherein said second spring is stressed a predetermined amount when said latch means is effective to restrain said actuating member, a second releasable latch means for holding said cam follower in said position once it has been moved to said position, a second cam for releasing said first latch means, a shaft for said cams, means for driving said shaft at a predetermined rate of speed, said cams being mounted for rotation on said shaft, a cam driving member fixed to said shaft for rotation therewith, independent adjusting means for each of said cams, each of said adjusting means having a portion fixed to one of said cams and having a second portion adapted to releasable clamping engagement with said driving member, whereby said cams may be angularly adjusted with respect to said shaft in such manner that said first 'cam acts first to stress said stronger spring and whereby said second cam may be adjusted with relation to said first cam thereby permitting selection of the interval between the time at which said stronger spring is stressed and the time at which said second cam effects the release of said first latch means, and means responsive to a predetermlned pressure for effecting the release of said second latch means.

4. In a device of the kind described, a control member, a movable actuating member operatively associated with said control member, a first spring for urging said actuating member in one direction, a first releasable latch means operative to restrain movement of said actuating member in 10 an opposite direction once it has been moved to a predetermined position by said first spring, a cam follower, a second stronger spring operatively connected at one end to said cam follower and at its other end to said actuating member, a first cam for moving said cam follower in a direction to stress said second spring in opposition to said first spring, and for moving it to a position wherein said second spring is stressed a predetermined amount when said latch means is effective to restrain said actuating member, a second releasable latch means for holding said cam follower in said position once it has been moved to said position, a second cam for releasing said first latch means, said cams being arranged to act in the order recited, a power operated chronometric device, a member driven by said chronometric device, means for adjustably connecting said cams to said driven member whereby the interval between any instant and the time at which said second cam effects the release of said first latch means may be selected, and means responsive to a predetermined pressure. for effecting the release of said second latch means.

5. In a device of the kind described, a control member, a movable actuating member operatively associated with said control member, a firstspring for urging said actuating member in one direction, a first releasable latch means opera-.

tive to restrain movement of said actuating memher in an opposite direction once it has been moved to a predetermined position by said first spring, a cam follower, a second stronger spring operatively connected at one end to said cam follower and at its other end to said actuating member, a first cam for moving said cam follower in a direction to stress said second spring in opposition to said first spring, and for moving it to a position wherein said second spring is stressed a predetermined amount when said latch means is effective to restrain said actuating member, a second releasable latch means for holding said cam follower in said position once it has been moved to said position, a second cam for releasing said first latch means, said cams being arranged to act in the order recited, a power operated chronometric device, a member driven by said chronometric device, means for adjustably connecting said cams to said driven member whereby the interval between any instant and the time at which said second cam eifectsthe release of said first latch means may be selected, a pressure responsive device operatively associated with said second latch means and arranged to effect the release thereof in-=.;response to an increase in fiuid pressure, and adjustable spring means for opposing the action of said pressure responsive device until a preselected pressure has been reached.

6. In a device of the kind described, a control member, a pivoted actuating lever operatively associated with said controlmember, a first spring for urging said actuating lever in one direction,

releasable latch means operative to restrain w movement of said lever in an opposite direction once it has been moved to a predetermined position by said first spring, a cam follower, a second stronger spring operatively connected at one end to said cam follower and at its other end to said actuating lever and being capable when stressed of readily overcoming said first spring, a first rotating cam for moving said cam follower in a direction to stress said second spring in opposition to said first spring when said latch means is effective, a second cam for releasing said latch means, and means for driving said cams at a predetermined rate of speed, said cams being arranged to act in the order recited, whereby said second spring is first stressed between said cam follower and said lever by said first cam and whereby thereafter said latch means is released by said second cam permitting said stressed second spring to move said actuating lever in an opposite direction with a snap action against said first weaker spring.

7. In a device of the kind described. a control member, a first spring means for biasing said control member in a first position, a pivoted actuating lever arranged to engage said control member and to move it oppositely to a second position whensaid lever is moved in one direction, a second stronger spring for moving said lever in said direction. releasable latch means operative to restrain movement of said lever in an opposite directlon once it has moved said control member to its second position, a cam follower. a third spring stronger than said second spring operatively connected at one end to said cam follower and at its other end to said actuating lever and being capable o! readily overcoming said second 25 1,233,692

spring when stressed, a first rotating cam for moving said cam follower in a direction to stress said third spring in opposition to said first spring when said latch means is effective, a second rotating cam for releasing said latch means, and means for rotating said cams at a predetermined rate of speed, said cams being arranged to act in the order recited, whereby said third spring is first stressed between said cam follower and said lever by said first cam and whereby thereafter said latch means is released by said second cam permitting said stressed third spring to move said actuating lever oppositely with a snap action against said second spring and permitting said control member to be moved in a snap action to its first position by said first spring.

CARL A. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED s'rxms PA'I'ENTS Name Date Nicholaus July 17, 1917 Number 

